BioMedical Admissions Test (BMAT) Practice Test 2025 - Free BMAT Practice Questions and Study Guide

The correct answer to the effect of chloride ions on damp litmus paper involves the bleaching action of the chloride ion. When litmus paper is damp and comes into contact with solutions containing strong oxidizing agents, chloride ions can participate in reactions that lead to the bleaching of the paper.

Chloride ions, particularly in the form of sodium hypochlorite or other reactive chlorine compounds, have the ability to oxidize the dyes in the litmus paper. This oxidation reaction alters the chemical structure of the dye, resulting in the loss of its color and thus leading to a whiter appearance of the paper.

In the context of other possible effects, litmus paper does not turn blue or red due to chloride ions, as these responses are characteristic of acid (turns blue litmus red) and base (turns red litmus blue) reactions rather than reactions with chloride. Furthermore, stating that chloride ions do not affect damp litmus paper is inaccurate, as the bleaching effect demonstrates a distinct change due to the presence of these ions. Thus, the bleaching action is the key reason this choice is the correct and most appropriate response.